Various types of contact probes have been used for electrically testing printed circuit boards and semiconductor devices. The electroconductive contact unit used in such conventional contact probes typically comprises a compression coil spring retained in a holder, and a pair of needle members received coaxially in the holder and resiliently projecting from either end of the holder. Normally, the needle members are electrically connected to the compression coil spring by soldering so that an electric signal received from one of the needle members is transmitted to the other needle member involving a relatively small electric resistance.
However, when the signal to be transmitted consists of a high frequency signal, the electric signal is required to be conducted by the compression coil spring, and the electric inductance of the coil spring may cause an undesired impedance to the electric signal.
Recently with the increase in the frequency of the signals that are required to be processed by semiconductor devices, it has become customary to use high frequency signals of up to several hundred MHz for testing semiconductor devices and printed circuit boards. As a result, there has been an increasing demand for the capability of such electroconductive contact units to handle such high frequency signals. In other words, the inductance and resistance of such electroconductive contact units are required to be reduced more than before.
Also, such electroconductive contact units are required to be compact in size so as to be arranged extremely close to each other, and to be provided with a sufficient resiliency so as to accommodate any irregularities in the surface states of the parts to be contacted.